Tuesday, May 8, 2012

Liking Links

I like the link.

Links by Clips
by RambergMediaImages
This may seem an uncontroversial position to take. But I'm specifically talking about the HTML link element. It is a nice model for expressing relationships between the current document and other resources. It has been imported into various XML standards (such as ATOM and NewsML-G2). But it isn't the only way to express links. Even in HTML, it is much more common to use

 <a href="">


<link href="" rel="related">.
Chain Links
by MyTudut
The Linky Landscape
In fact, there are a range of types of links. If you think about the img element within HTML, it includes a reference to a remote object to include in a web page (via the img/@src attribue). Even though the img element uses an HTTP reference, it isn't very linky - it is more about composing a document from multiple resources of different types.

 by Leo Reynolds
Anchors Aweigh!
The HTML a (anchor) element is a big step up in linkyness. It is generally used to specify an outbound navigational link from the current HTML page to some other resource (such as another HTML page, but it could also be a video clip, an image or anything else that can be addressed via a URL). But the HTML a element lets you specify how the remote resource relates to the current page: the a/@rel attribute lets you specify the relationship from the current document to the destination resource. Similarly, the a/@rev attribute lets you express the reverse relationship - how the remote resource relates to this document. (Remember, not all relationships are symmetrical). So, the anchor tag has some nice (though, in practice, rarely used) attributes for specifying in a machine-readable, controlled way the relationships between web resources. One limitation of the HTML a element is that it is only for use for "inline" links - such as marking up a bit of text within a paragraph.
by Profound Whatever
The link element has all the same attributes as the anchor element but it is designed to be purely semantic - it simply defines a relationship between the current document and the resource referred to in the link/@href attribute. The link element cannot contain content and so it is purely about referencing another addressable resource. As with the HTML a element, the relationship between the document containing the link and the resource being referenced can be specified using the @rel and @rev attributes.
by rubygold
Web Link Types
In an effort to provide some shared semantics about types of links, IANA put together a small, but growing, list of link types - values that you can use in your @rel or @rev attributes. Whenever you are adding a link to your document, check out the existing list of link relations, to see if you can provide some hints as to the relationship between your document and the linked resource:

Chain Links
by Eric M Martin
Spreading the Link
In fact, the HTML link element has proven so useful, that it has been adopted into other markup standards, notably IETF's ATOM and IPTC's NewsML-G2. The IETF issued RFC 5988 specifically about linking, not simply in the context of HTML documents.

So, if you need to establish relationships between resources, then consider using the link element, with @rel or @rev values. And if you happen to be designing a markup language, my advice is to make sure you include the full link element. I predict you'll find it useful over and over again.

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